1. Field of the Invention
The present invention relates to a hydraulic circuit that can prevent a bucket from being separated from a bucket rest during traveling of wheel type heavy equipment.
More particularly, the present invention relates to a hydraulic circuit to prevent a bucket separation from a bucket rest during long traveling of heavy equipment, which can prevent the bucket from being separated from the bucket rest by preventing a change of stroke of a boom cylinder or an arm cylinder during long traveling of the heavy equipment, and can secure safe driving since it is not required for an operator to adjust the position of boom and arm.
2. Description of the Prior Art
As illustrated in FIG. 1, a conventional hydraulic circuit includes first and second hydraulic pumps 1 and 2; actuators (e.g., a boom cylinder 3 and a bucket cylinder 4) installed in a flow path of the first hydraulic pump 1 to be driven during shifting of a spool 12 for the boom cylinder and a spool 18 for the bucket cylinder; actuators (e.g., a traveling motor 5, a swing motor 6, and an arm cylinder 7) installed in a flow path of the second hydraulic pump 2 to be driven during shifting of a spool 11 for the traveling motor, a spool 19 for the swing motor, and a spool 13 for the arm cylinder; a main control valve 8 installed in flow paths between the first and second hydraulic pumps 1 and 2 and the actuators to control a start, a stop, and a direction change of the corresponding actuators during shifting of the spools; and a boom confluence logic valve 10 installed in a confluence flow path 9 of the first and second hydraulic pumps 1 and 2 to make hydraulic fluid of the second hydraulic pump 2 join hydraulic fluid of the first hydraulic pump 1 being supplied to the boom cylinder 3 during shifting of a poppet inside the boom confluence logic valve 10.
If a manipulation lever (RCV) (not illustrated) is operated to lift up a boom, a poppet of the boom confluence logic valve 10 is shifted upward as shown in the drawing. Accordingly, the hydraulic fluid fed from the second hydraulic pump 2 joins the hydraulic fluid fed from the first hydraulic fluid 1 via the boom confluence logic valve 10, and the confluent fluid is supplied to a large chamber of the boom cylinder 3. Accordingly, the boom is rapidly lifted up to perform a smooth operation.
By contrast, if the boom-up operation is not performed, the confluence flow path 9 is blocked by the poppet of the boom confluence logic valve 10, and thus the supply of the hydraulic fluid from the second hydraulic pump 2 to the boom cylinder 3 is intercepted.
In the case where a wheel type heavy equipment travels for a long time to be used as a transportation means for moving to a workplace, the hydraulic fluid fed from the second hydraulic pump 2 by the operation of a traveling lever (or traveling pedal) is supplied to the traveling motor 5 via the spool 11 for the traveling motor. Other spools 12, 13, 18, and 19 for working devices, except for the spool 11 for the traveling motor, are kept in a neutral state.
At this time, since the boom confluence logic valve 10 is in a closed state, but the hydraulic fluid fed from the second hydraulic pump 2 is kept at high pressure, the hydraulic fluid is supplied to an inlet port of the spool 12 for the boom cylinder via an orifice of the boom confluence logic valve 10.
A very small amount of hydraulic fluid leaking through a gap between a land part of the spool 12 for the boom cylinder and the housing is supplied to a large chamber 3a of the boom cylinder 3. Accordingly, the boom is lifted up during traveling of the heavy equipment against an operator's intention.
Specifically, during long traveling of the equipment, a part of hydraulic fluid fed from the second hydraulic fluid 2 to the traveling motor 5 is supplied to the large chamber 3a of the boom cylinder 3 via the orifice of the boom confluence logic valve 10, and this causes the boom to be lifted up.
In addition, a part of high-pressure fluid fed from the second hydraulic pump 2 is also supplied to the arm cylinder 7 due to the leakage through the gap between the land part of spool and the housing, and thus the arm cylinder 7 is driven to be in an arm-in or arm-out state.
If the boom is lifted up due to the stroke change of the boom cylinder 3 or the arm is driven due to the stroke change of the arm cylinder 7 during long traveling of the heavy equipment in a state that the bucket is placed on the bucket rest (not illustrated), the bucket is separated from the bucket rest to allow free movement of the bucket, and this may disturb the operator's driving comfort & safety of the heavy equipment.
In this case, the operator may operate the boom to place the bucket in the bucket rest by changing a mode switch from a traveling mode to a working mode, and then change again the mode switch from the working mode to the traveling mode to resume the traveling of the heavy equipment. However, this may cause a safety accident to occur during traveling of the heavy equipment with the lowering of driveability.